Breast pumps are used by mothers to collect milk in those occasions when natural breastfeeding is not possible. These include physical separation between the mother and the infant (i.e. hospitalized mother or infant), physiological difficulties related to the mother or the infant (i.e. oversensitive breasts, premature infant etc.), social separation between the mother and the infant (i.e. working mothers) etc.
A healthy child sucks usually at a frequency of about 15 to 60, generally 40 to 60, and in average 50 cycles per minute. Usually the infant sucks faster at the beginning to stimulate the breast until milk starts to flow and then sucks constantly at a more or less constant speed. The suction cycle of the infant consists of three parts, first with the building-up of vacuum through suction during which milk is extracted from the breast, then by breaking the vacuum by allowing air into the mouth through the mouth or the nose and finally by swallowing the milk and breath.
A breast pump, being complementary to the natural breastfeeding, should offer the mother the best possible simulation of the natural breastfeeding process. Some pumps simulate the suction cycle of the infant manually or semi-automatic, usually through manual breaking of the vacuum by the mother. The disadvantage of this, however, is that with these pumps each suction cycle takes several seconds to be completed and therefore leads to a cycle speed much lower than the cycle speed of a healthy infant. Other pumps use auto-cycle suction systems that simulate better the natural feeding process. Here too, even in the most sophisticated pumps conceivable which include a speed regulation, the suction strength is not constant, but depends on the suction speed.
Another approach is has been suggested in the copending PCT Application No. WO 98/26817. There is a flow regulator which supplies by-passing additional air into the suction pathway. However, it has been found out that with such an arrangement it is not possible to maintain constant conditions with respect to air flow's intensity, if one would attempt to vary the speed of the driving motor in order to modify the suction frequency.